ABSTRACT
Objective To investigate the optimization of therapeutic regimen through the adjustment of the minimum sub-field area in intensity-modulated radiotherapy (IMRT) for cervical cancer,under the premise of no influence on the dose to target volume or organs at risk.Methods A total of 12 patients with pathologically confirmed cervical cancer were enrolled,and the prescribed dose to the planning target volume (PTV) was 50 Gy in 25 fractions.The Pinnacle 8.0m treatment planning system was used for all patients,and 16 IMRT plans were developed for each patient,with the application of 9 evenly distributed fixed incidence directions (0°,40°,80°,120°,160°,200°,240°,280°,and 320°),a minimum sub-field number of 80,and a minimum sub-field hop count (MU) of 5 MU.The range of sub-field area was 2-81 cm2.Direct machine parameter optimization was used for inverse-planned optimization calculation,and all the plans met the requirements of the clinical prescribed dose.The dose-volume histogram was used to evaluate the dose distribution in target volume and organs at risk.Results With the sub-field area increasing from 2 cm2 to 81cm2,the total hop count of IMRT plan was reduced from (1405±170) MU to (490±47) MU (P=0.000),and when the sub-field area increased above 6 cm×6 cm,the total hop count was reduced significantly (P=0.000).In the IMRT plan with a minimum sub-field area of 2-49 cm2,there was no significant difference in dose between the target volume and the organs at risk (P＞0.05).The dose to the rectum,the bladder,and both femoral heads showed no significant differences across the IMRT plans with different minimum sub-field areas (P＞0.05).Conclusions When the Pinnacle 8.0m treatment planning system is used to develop IMRT plans for cervical cancer,the requirements for clinical dose can still be met with a minimum sub-field area reaching 7 cm×7 cm,and there are significant reductions in sub-field hop count and total hop count.
ABSTRACT
Objective To study the dosimetry characteristics of 9 equal spaced fields and 9 fields with beam angle optimization (BAO) process for cervix uteri.Methods 12 cervix uteri cancer patients CT Images were transferred into Eclipse planning system.Each patient,the 9 equal spaced fields and 9 fields by BAO process were IMRT plan designed with the same CT image.Make a evaluation of dose distribution for target volume and OARs,and paired t test for them.Results Comparing to 9 equal spaced fields IMRT plan,the quality of 9 fields IMRT plan with BAO process the the PTV V95％ was 99.31％ vs 99.42％,P =0.020,at the same time V105％,V110％,Dmax,D got 60.54％ vs 47.92％,P =0.013;7.14％ vs 0.37％,P =0.000;56.62 Gy vs 55.47 Gy,P =0.000;53.29 Gy vs 52.72 Gy,P =0.000,the CI and HI was 0.85 vs 0.89,P =0.000 ;0.10 vs 0.13,P =0.000.For organs at risk,bladder V40 was increased by 4.7 ％ (P =0.013) ;the D40 of rectum was 0.5 Gy higher (P =0.004) ; the small bowel's DVH showed that V40 and Dmax increased by 0.6％ (P =0.015) and 1.4 Gy (P =0.000),D of bone marrow were raised separately by 1.3 Gy (P =0.000),the spinal cord's dose D0.1 cm3 was also increased by 2.0 Gy (P =0.000).Conclusion The quality of 9 equal spaced fields IMRT plan will be better than those achieved by BAO process optimized plans.